(1) Field of the Invention
This invention relates to a system for the projection of cinematographic works or digital works with sound, and more specifically for such films with at least one sound channel, the said system comprising a screen and, for the said sound channel, at least one woofer and at least one medium/treble speaker. Hereinafter, sound channel will refer only to the screen channels, not including the environment channels which, in the invention, are treated in the conventional manner.
(2) Prior Art
There are normally three screen channels: a left channel, a central channel and a right channel. There are also systems with five channels including a middle-left channel and a middle-right channel.
Finally, there are giant-screen systems with four channels, two of which are lateral channels and the other two are a central-high channel and a central-low channel.
In conventional systems, each channel comprises two or three speakers, namely, in every case, a woofer and either a medium/treble speaker or one mid-range speaker and one tweeter. The medium/treble speaker, mid-range speaker and tweeter are generally horn speakers. These speakers are placed behind the screen.
Due to this layout, it becomes necessary to use perforated screens, made from a sheet of PVC provided with perforations or microperforations. In fact, although a non-perforated screen allows the bass through with no difficulties, it causes an unacceptable attenuation of the mediums, trebles and extreme trebles.
Perforated screens however, have a certain number of disadvantages in terms of sound and also degrade the quality of the image. In terms of the sound, the perforated screen introduces a mask effect as well as interference due to the dispersion of the sound waves passing through the perforations. In terms of the image, the perforations considerably reduce the brightness, contrast and definition. In addition, in the first rows of the projection room, the perforations are visible as a weft.
Document U.S. Pat. No. 5,025,474 already suggests using a projection screen as an acoustic diaphragm directly activated by magnetic actuators. However, such an arrangement is only possible for smaller-sized screens. In addition, the mediums and trebles cannot be suitably reproduced using this system.
Documents U.S. Pat. No. 5,004,067 and U.S. Pat. No. 5,109,423 also suggest using a non-perforated screen and placing medium/treble horn speakers above the screen. This arrangement has the serious drawback of shifting the sound image completely upwards, out of the screen for the most part.